An aim of the present invention is to improve the performance of the mechanical movement of a timepiece, particularly that of a mechanical timepiece. The balance spring, long used as an oscillator in mechanical watches, has proved its worth, but in spite of, or maybe because of, centuries of research and development, it is possible that it is nearing its limits. Hence, the best balance springs achieve a quality factor Q of about 300. With the quality factor of an oscillator being defined by the equation Q=2π×(energy stored/energy loss per period), it essentially represents the number of oscillations after which the oscillator loses its entire energy and stops.
The tuning fork is well known for its time base qualifies; the tuning fork movement wristwatches of the 1960's were the most accurate in the world until the advent of the quartz watch. Max Hetzel is the originator of many patented inventions relating to use of a tuning fork as an oscillator, resulting in production of the Accutron wristwatch (registered trademark), marketed by the company Bulova Swiss SA.
The Accutron watch however comprises an electronic resonator since each branch of the tuning fork bears a permanent magnet associated with an electromagnet rigidly mounted on the frame of the watch. The operation of each electromagnet is slaved to the vibrations of the tuning fork by means of the magnets that it bears, such that the vibrations of the tuning fork are sustained by the transmission of periodic magnetic pulses of the electromagnets to the permanent magnets. One of the branches of the tuning fork actuates a ratchet making it possible to rotate the mobiles of the going train of the watch.
U.S. Pat. No. 2,971,323 for example, derived from an application dating from 1957, describes a mechanism only suitable however for producing a purely mechanical watch, i.e. devoid of electronic circuits. A genuine need in fact exists, in terms of market, for purely mechanical timepieces displaying an increased precision of watch operation in relation to the known pieces.
An overall difference between mechanical wristwatches and acoustic tuning fork-based electronic watches lies in the fact that in the latter, the oscillator as the timekeeper also serves as an energy distributor, i.e. the oscillations are used to power the movement (Accutron) or determine the activity of an electric motor that acts on the watch hands (quartz-based electronic watch). In mechanical watches on the other hand, regulation is performed at the end of the energy transmission chain.
U.S. Pat. No. 3,208,287, derived from an application dating from 1962, describes a resonator comprising a tuning fork coupled to an escapement wheel by means of magnetic interactions. More specifically, the tuning fork bears permanent magnets interacting with the escapement wheel, with the latter being made of magnetic conductive material. The escapement wheel is cinematically connected to an energy source, which may be mechanical or adopt the form of a motor, while it has openings in its thickness such as to form a variable reluctance magnetic circuit when driven in rotation, in relation to the magnets borne by the tuning fork. This patent discloses “abnormal oscillation, illustrated in FIG. 9. This in fact involves symmetrical oscillation which, according to this patent, can be avoided by positioning the escapement wheel so as to act, simultaneously, on both prongs of the oscillator, as shown in FIGS. 2 and 3. This solution resembles that used in quartz-based electronic watches (and likewise in the Accutron watch mentioned above) in that the symmetrical mode of oscillation is imposed by the simultaneous impulsion of both prongs.
In relation to U.S. Pat. No. 3,208,287, the present invention seeks to solve several technical problems. On the one hand, it is desired to induce an antisymmetrical oscillation by acting on a single prong of the tuning fork; therefore, without imposing antisymmetrical oscillation by simultaneous impulsion of both prongs. On the other hand, use of magnets to distribute the energy to an oscillator (impulsion by escapement) or moreover to regulate an energy is not strictly speaking “mechanical”, for the simple reason that the energy is transmitted by magnetic forces and is therefore associated with electromagnetic phenomena.
This same reasoning is valid for the teaching of European patent application EP 2 466 401.
In the light of the above, the present invention aims to provide a mechanical movement watch comprising a more accurate time base than that of the conventional balance spring. It is therefore an aim of the present invention to offer an oscillator characterised by a quality factor higher than that of the balance spring.
In particular, an aim of the invention is to provide a wristwatch with entirely mechanical movement using a tuning fork oscillator as the time base.
An aim of the present invention is to avoid, in a tuning fork oscillator, the symmetrical oscillations. More specifically, the present invention aims to avoid the symmetrical oscillations in an oscillator comprising a material characterised by low internal friction, in order to make the oscillator able to perform said symmetrical oscillations.
An aim of the invention is to provide a tuning fork based on a material having low internal friction, such as monocrystalline silicon. Use of such a material allows an increase in the quality factor Q of the oscillations, but makes the tuning fork able to perform symmetrical oscillations not desired within the context of a time base.
An aim of the present invention is to make available an oscillator in which the antisymmetrical oscillations are encouraged, even if the impulses are transmitted to one of the prongs only; in other words, in the absence of impulses simultaneous to both prongs.
The present invention seeks to solve the above problems and offers other advantages that will appear more clearly upon reading the description and the claims.
Summary of Invention
In an aspect, the present invention relates to a timepiece comprising a mechanical clock movement comprising: a tuning fork oscillator, wherein said oscillator comprises an assembly having two prongs and a base connecting said prongs, wherein said oscillator comprises a rod connected to said base, the oscillator being connected by its rod to a fastening member connected to the movement, wherein said assembly comprises or consists of a material A, said material A being characterised by low internal friction, wherein said movement comprises a mechanical impulsion element able to act on one of the two prongs so as to induce and sustain oscillation of said oscillator, wherein said oscillator is able to oscillate both in a desired antisymmetrical mode and in an unwanted symmetrical mode, characterised in that the quality factor Q2 of the symmetrical oscillation mode of said oscillator is reduced in relation to the quality factor Q1 of the antisymmetrical oscillation mode.
In an aspect, the present invention relates to a tuning fork oscillator, wherein said oscillator comprises an assembly having two prongs and a base connecting said prongs, wherein said oscillator comprises a rod connected to said base, the oscillator being connected by its rod to a fastening member connected to a support, wherein said assembly is formed of a material A, characterised by low internal friction, wherein said oscillator is able to oscillate both in a desired antisymmetrical mode and in an unwanted symmetrical mode, characterised in that the quality factor Q2 of the symmetrical oscillation mode of said oscillator is reduced in relation to the quality factor Q1 of the antisymmetric oscillation mode.
In an aspect, the present invention relates to a tuning fork oscillator, wherein said oscillator comprises two prongs and a base connecting said prongs, wherein said oscillator comprises a rod connected to said base, characterised in that, in said oscillator, a symmetrical oscillation mode is damped or prevented by the presence of a material selected in or on said oscillator and/or in or on a fastening of the oscillator.
In an aspect, the present invention relates to a tuning fork oscillator, wherein said oscillator comprises two prongs and a base connecting said prongs, wherein said oscillator comprises a rod connected to said base, the oscillator being connected by its rod to a fastening, wherein said oscillator is manufactured from one or several materials rendering said oscillator able to perform symmetrical oscillations and wherein said oscillator or the fastening furthermore comprise another material able to damp said symmetrical oscillations.
In an aspect, the present invention relates to a tuning fork oscillator, wherein said oscillator comprises two prongs and a base connecting said prongs, wherein said oscillator comprises a rod connected to said base, the oscillator being connected by its rod to a fastening, wherein said oscillator comprises or is manufactured from several materials including a material A and a material A′, wherein material A′ is characterised by a thermal expansion coefficient of opposite sign to that of material A.
In an aspect, the present invention relates to a movement for a timepiece comprising the oscillator in addition to a timepiece including the oscillator.
In an aspect, the present invention relates to use of a material possessing a comparatively high internal friction in order to avoid symmetrical oscillation in a tuning fork oscillator.